The invention relates to new sulfur-functional polyorganosiloxanes, a process for their preparation and their use in rubber mixtures and for the production of mouldings.
The use of sulfur-containing organosilicon compounds such as 3-mercaptopropyltriethoxysilane or bis(3-[triethoxysilyl]propyl)tetrasulfane as silane coupling agents or reinforcing additives in rubber mixtures containing oxide filler for use as treads and other parts of automobile tires is known (DE 2 141 159, DE 2 212 239, U.S. Pat. No. 3,978,103, U.S. Pat. No. 4,048,206).
Furthermore, it is known that sulfur-containing silane coupling agents can be used in the production of sealing compounds, moulds for metal casting, paint coatings and protective coatings, adhesives, asphalt mixtures and for plastics containing oxide filler.
These coupling or bonding agents form bonds both with the filler and with the elastomer and consequently bring about a good interaction between the filler surface and the elastomer. They lower the mixing viscosity and facilitate the dispersion of the filler.
EP 0 784 072 A1 describes the use of a combination of a silane coupling agent and a functionalized polyorganosiloxane having at least one functional siloxyl group which can bond to the silica.
As a coupling agent in rubber mixtures, 3-mercaptopropyltriethoxysilane is able to produce an improved silica/elastomer coupling at a comparatively low dosage (U.S. Pat. No. 3,350,345, FR-A-2 094 859). However, owing to the high reactivity of the SH group and consequently the well-known tendency to form preliminary cross-linking as well as increased mixing viscosity, the workability of the mixtures and their industrial application are limited. It is also known that the addition of a protective additive consisting of a functional polyorganosiloxane having at least one functional siloxyl group decreases the reactivity, lowers the mixing viscosity and thus ensures that such rubber mixtures are workable (EP 0 784 072 A1).
From the economic aspect it is to be regarded as disadvantageous that, in addition to the silane coupling agents described in EP 0 784 072 A1, a siloxyl-functionalized polyorganosiloxane also has to be added to the rubber mixture.
Furthermore, it is known that the use of commercially available silane coupling agents (DE 22 55 577) having three alkoxy substituents on the silicon atom leads to the release of considerable quantities of alcohol during the mixing process.
It is therefore an object of the present invention to avoid problems of the prior art.
The above and other objects of the invention can be achieved by sulfur-functional polyorganosiloxanes corresponding to the general formula I corresponding to the general formula I 
wherein R1, R2, R3, R4, independently of one another, denote H, (C1-C4)alkyl, (C1-C4)alkoxy, (C1-C4) haloalkoxy, (C1-C4) haloalkyl, phenyl, aryl or aralkyl and
W denotes a group which can bond to the silica and preferably can be (C1-C4) alkoxy
or
(C1-C4) haloalkoxy and
Y denotes alkyl, haloalkyl, phenyl, aryl or aralkyl and
Z denotes an alkylidene group having 0-6 carbon atoms and
A denotes a group which can bond with at least one elastomer of the rubber mixture:
for q=1 preferably a mercapto group
(SH) and thiocyanate group (SCN) and for q=2 a disulfide (S2) and a polysulfide (Sx) with x=2-10 and H denotes hydrogen and
the sum of k+m+n+pxe2x89xa73 and also k and n can equal 0.
Preferred polyorganosiloxanes in connection with the invention which may be mentioned first of all are the following, built up from linear statistical, sequential or block polymers, in which R1, R2, R3 and R4=alkyl, in particular methyl, W=alkoxy, in particular ethoxy, Y=alkyl, in particular n-propyl, Z=alkylidene, in particular CH2CH2CH2, m and p=1-100, and k and n=0-50, with the sum of k+m+n+p=10-150, in particular 20-100.
In a preferred embodiment, R1, R2, R3, R4 can be methyl, W=ethoxy, Y=n-propyl, Z=CH2CH2CH2, A=mercapto (SH), thiocyanate (SCN) for q=1 and A=polysulfide (Sx) and disulfide (S2) for q=2 and k+m+n+p=10-150, in particular 20-100.
The polyorganosiloxanes according to the invention wherein A=Sx can be cyclic, branched or linear in form.
The compounds according to the invention can exist both as an individual compound having a defined molecular weight, and as a mixture of oligomers having a molecular weight distribution.
The compounds according to the invention corresponding to the general formula I can be easily prepared in two steps, by reacting compounds corresponding to the general formula II 
wherein R1, R2, R3 and R4 have the meanings given above and v can be a number between 2 and 150, with compounds corresponding to the general formula III 
wherein R5H, alkyl and X are fluorine, chlorine, bromine and iodine, preferably chlorine, and w is a number between 0 and 15, preferably w=1 and R5=H (allyl chloride) and also R5=methyl (methallyl chloride), under catalytic conditions by a mechanism of hydrosilylation using a catalyst from the family of the platinum metals, optionally in a solvent, and optionally at reaction temperatures between 20xc2x0 C. and 200xc2x0 C., at pressures between normal pressure or an excess pressure up to 6 bar, to form compounds corresponding to the general formula IV 
wherein R1, R2, R3, R4, X, Y, Z, m, n and p have the meanings given above.
In the second step, compounds corresponding to the general formula IV can be reacted with MSH, MSCN or M2Sx,
wherein M is a metal ion and x, on statistical average, can be a number between 2 and 10, or with M2S and S, wherein M is a metal ion, in an alcohol W-H, wherein W has the meaning given above, optionally at reaction temperatures between 20xc2x0 C. and 150xc2x0 C. and optionally under catalytic conditions, at normal pressure, to form the compounds according to the invention corresponding to the general formula I.
The compound corresponding to formula IV can advantageously be prepared as follows: A subequivalent quantity of a mixture consisting of a compound corresponding to formula III, wherein X, R5 and w have the meanings given above, and a platinum catalyst, preferably of the Karstedt type, are added without solvents, at normal pressure or excess pressure up to 6 bar, preferably at normal pressure, at temperatures between 20xc2x0 C. and 200xc2x0 C., particularly preferably 100xc2x0 C. to 150xc2x0 C., to a compound corresponding to formula II. The mixture is stirred for 1 h to 8 d, preferably 1 to 4 h, at normal pressure or excess pressure up to 6 bar, preferably at normal pressure, at temperatures between 20xc2x0 C. and 200xc2x0 C., particularly preferably 100xc2x0 C. to 120xc2x0 C., then the reaction is concluded and the new compounds of type IV remain behind, mostly in the form of viscous liquids.
The reactions can advantageously be carried out under absolute conditions, that is, with the exclusion of moisture.
Various hydrosilylation processes of the type described above are known from U.S. Pat. No. 3,159,601, EP-A-57 459, U.S. Pat. No. 3 419 593, U.S. Pat. No. 3,715,334, U.S. Pat. No. 3,775,452 (Karstedt).
Owing to the differing selectivities of the catalysts, there can be a resulting formation of the fragment corresponding to formula V 
wherein R4, X, Y and n have the meanings given above.
At a selectivity of 100%, n 0 in compound IV and in fragment V respectively.
In a second step, the compound according to the invention corresponding to formula I can advantageously be prepared as follows: A compound corresponding to formula IV, wherein R1, R2, R3, R4, W, X, Y, Z, m, n and p have the meanings given above is added to a suspension of MSH, MSCN or M2S and S, or to previously prepared M2Sx, in an alcohol W-H. Hydrogen gas is formed in this process. The reaction is heated for 1 h to 8 d, preferably 1 to 24 h, at normal pressure, to temperatures between 20xc2x0 C. and 150xc2x0 C., particularly preferably at the boiling point of the alcohol W-H and, on conclusion of the reaction, the precipitate formed is filtered off. After the removal of the excess alcohol W-H, the new compounds of type I generally remain behind in the form of viscous liquids or low-melting solids.
The alcoholysis and sulfur-functionalization take place simultaneously in the process according to the invention. No additional catalyst is required for the alcoholysis. In the case of complete alcoholysis, k=0 in compound I. In addition, the Sixe2x80x94X group in fragment V is simultaneously converted to Sixe2x80x94W.
Ammonium ions, sodium ions or potassium ions can be used as the preferred metal ions. In this connection, the use of the corresponding sodium compound is particularly preferred.
Various sulfidation processes of the type described above are known and are described in JP 722 8588, U.S. Pat. No. 54 05 985 and U.S. Pat. No. 54 66 848.
The term xe2x80x9calkylxe2x80x9d means both xe2x80x9cstraight-chainxe2x80x9d and xe2x80x9cbranchedxe2x80x9d alkyl groups. The term xe2x80x9cstraight-chain alkyl groupxe2x80x9d means, for example, groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl; xe2x80x9cbranched alkyl groupxe2x80x9d means groups such as, for example, isopropyl or tert butyl. The term halogen means fluorine, chlorine, bromine or iodine. The term xe2x80x9calkoxyxe2x80x9d denotes groups such as, for example, methoxy, ethoxy, propoxy, butoxy, isopropoxy, isobutoxy or pentoxy.
Within the scope of the invention, xe2x80x9carylxe2x80x9d means phenyls, biphenyls, phenols or other benzenoid compounds substituted with (C1-C6)alkyl-, (C1-C6)alkoxy-, halogen, or with hetero atoms such as N, O, P or S. xe2x80x9cArylalkylxe2x80x9d means that the xe2x80x9carylsxe2x80x9d indicated above are bonded to the relevant silicon atom by a (C1-C6) alkyl chain, which for its part can be (C1-C4)alkyl- or halogen-substituted. If xe2x80x9carylxe2x80x9d contains a hetero atom such as O or S, the (C1-C6) alkyl chain can also form a bond with the silicon atom via the hetero atom.
Where substituents such as, for example, (C1-C4) alkoxy are named, the number shown as a subscript indicates the total number of carbon atoms in the group.
The advantage of the multifunctional polyorganosiloxanes according to the invention is a use as silane coupling agents in silica-reinforced rubber mixtures, wherein they have at least one functional siloxyl group, which is able to form a chemical and/or physical bond with the hydroxyl groups at the surface of the silica particles, and contain at least one sulfur functionality, which is capable of chemical bonding to the polymer chains. As a result of the smaller proportion of alkoxy functions compared with prior art, the use of the multifunctional polyorganosiloxanes according to the invention also leads to a diminished release of alcohol during the mixing process.
The sulfur-functional polyorganosiloxanes according to the invention are particularly suitable for use in rubber mixtures.
After the application of the process according to the invention, rubber mixtures which contain the sulfur-functionalized polyorganosiloxanes according to the mouldingsxe2x80x94in particular pneumatic tires or tire treadsxe2x80x94resulting from a vulcanization step exhibit a low rolling resistance with at the same time a good wet adhesion and high abrasion resistance.
The present invention also provides rubber mixtures which contain the sulfur-functional polyorganosiloxanes according to the invention. The rubber mixtures can also contain rubber, fillers, in particular also precipitated silica and optionally other rubber auxiliaries, and at least one sulfur-functional polyorganosiloxane according to the invention, in quantities of 0.1 to 15 wt. %, particularly preferably 5-10 wt. %, based on the quantity of the oxide filler used.
Where the sulfur-functional polyorganosiloxanes according to the invention are used in rubber mixtures, there are found to be advantages over the known mixtures as regards the static and dynamic vulcanization data.
The sulfur-functional polyorganosiloxanes according to the invention and the fillers are preferably added at composition temperatures of 80 to 200xc2x0 C. But they can also be added later at lower temperatures (40 to 100xc2x0 C.) for example, together with other rubber auxiliaries.
The sulfur-functional polyorganosiloxanes according to the invention can be introduced into the mixing process either in pure form or applied to an inert organic or inorganic support. Preferred supporting materials are silicas, natural or synthetic silicates, aluminium oxide or carbon blacks.
Suitable fillers for the rubber mixtures according to the invention are:
Carbon blacks: The carbon blacks to be used here are produced by the lampblack, furnace or channel black process and have BET surface areas of 20 to 200 m2/g. The carbon blacks may optionally also contain hetero atoms such as, for example, Si.
Highly dispersed silicas, prepared, for example, by precipitation from solutions of silicates or flame hydrolysis of silicon halides, having specific surfaces of 5 to 1000, preferably 20 to 400 m2/g (BET surface area) and primary particle sizes of 10 to 400 nm. The silicas may optionally also be present as mixed oxides with other metal oxides, such as the oxides of Al, Mg, Ca, Ba, Zn and titanium.
Synthetic silicates, such as aluminum silicate; alkaline-earth silicates, such as magnesium silicate or calcium silicate, having BET surface areas of 20 to 400 m2/g and primary particle diameters of 10 to 400 nm.
Natural silicates, such as kaolin and other naturally occurring silicas.
Glass fibres and glass fibre products (mats, strands) or glass microbeads.
It is preferable to use carbon blacks having BET surface areas of 20 to 400 m2/g or highly dispersed silicas, prepared by precipitation from solutions of silicates, having BET surface areas of 20 to 400 m2/g in quantities of 5 to 150 parts by weight, in each case based on 100 parts rubber.
The above-mentioned fillers can be used alone or in a mixture. In a particularly preferred embodiment of the process, 10 to 150 parts by weight of light-coloured fillers, optionally together with 0 to 100 parts by weight carbon black, and 0.1 to 15 parts by weight, preferably 5 to 10 parts by weight, of a compound corresponding to formula I, in each case based on 100 parts by weight of the filler used, may be used for the preparation of the mixtures.
Besides natural rubber, synthetic rubbers are also suitable for preparing the rubber mixtures according to the invention. Preferred synthetic rubbers are described, for example, in: W. Hofmann, Kautschuktechnologie, Genter Verlag, Stuttgart 1980. They include:
Polybutadiene (BR)
Polyisoprene (IR)
Styrene/butadiene copolymers having styrene contents of 1 to 60 wt. %, preferably 2 to 50 wt. % (SBR)
Isobutylene/isoprene copolymers (IIR)
Butadiene/acrylonitrile copolymers having acrylonitrile contents of 5 to 60, preferably 10 to 50 wt. % (NBR)
partially hydrogenated or completely hydrogenated NBR rubber (HNBR)
Ethylene/propylene/diene copolymers (EPDM)
and mixtures of these rubbers. In particular, anionically polymerised L-SBR rubbers having a glass temperature of above xe2x88x9250xc2x0 C. as well as mixtures of these with diene rubbers are of interest for the production of tires for automobiles.
The rubber vulcanizates according to the invention can also contain other rubber auxiliaries, such as reaction accelerators, antioxidants, heat stabilizers, light stabilizers, antiozonants, processing aids, plasticizers, tackifiers, blowing agents, dyes, waxes, extenders, organic acids, retarders, metal oxides and activators, such as triethanolamine, polyethylene glycol, hexanetriol, which are known in the rubber industry.
The rubber auxiliaries are used in conventional quantities, which depend inter alia on the intended use. Conventional quantities are, for example, quantities of 0.1 to 50 wt. %, based on rubber. The sulfur-functionalized polyorganosiloxanes can be used on their own as cross-linking agents. As a rule, the addition of other cross-linking agents is recommended. Other known cross-linking agents which can be used are sulfur or peroxides. The rubber mixtures according to the invention can in addition contain vulcanization accelerators. Examples of suitable vulcanization accelerators are mercaptobenzothiazoles, sulfenamides, guanidines, thiurams, dithiocarbamates, thioureas and thiocarbonates. The vulcanization accelerators and sulfur or peroxides are used in quantities of 0.1 to 10 wt. %, preferably 0.1 to 5 wt. %, based on rubber.
The vulcanization of the rubber mixtures according to the invention can take place at temperatures of 100 to 200xc2x0 C., preferably 130 to 180xc2x0 C., optionally under pressures of 10 to 200 bar. The mixing of the rubbers with the filler, optionally with the rubber auxiliaries and with the sulfur-functionalized polyorganosiloxanes according to the invention can be carried out in conventional mixing units, such as rolls, closed mixers and mixer-extruders. The rubber vulcanizates according to the invention are suitable for the production of mouldings, for example, for the production of pneumatic tires, tire treads, cable sheaths, hoses, drive belts, conveyor belts, roller coatings, tires, shoe soles, sealing rings and damping elements.